The invention concerns an image processing method for displaying objects with reflective surfaces, wherein each object is composed of at least one polygonal plane represented by a first parameter set that represents the spatial position of the polygonal plane, and including the steps of: calculating, from the first parameter set for each object, a second parameter set (n.sub.x, n.sub.y, n.sub.z) representing the spatial position of a planar normal of the polygonal plane; and calculating, from the second parameter set and a third parameter set (e.sub.x, e.sub.y, e.sub.z) representing a perspective of a predetermined viewer of the polygonal plane, a fourth parameter set representing a spatial position of a light ray reaching the viewer after being reflected at the polygonal plane.
The invention further relates to an image processing arrangement for displaying objects, wherein each object is composed of at least one polygonal plane represented by a first parameter set that represents the spatial position of the polygonal plane, including: means for calculating, from the first parameter set for each object, a second parameter set (n.sub.x, n.sub.y, n.sub.z) representing a spatial position of a planar normal of the polygonal plane; and means for calculating, from the second parameter set and a predetermined third parameter set (e.sub.x, e.sub.y, e.sub.z) representing a perspective of a viewer of the polygonal plane, a fourth parameter set representing a spatial position of a light ray reaching the viewer after being reflected at the polygonal plane.
In computer graphics systems, bodies are generally reproduced with grid models, which are described by the space coordinates of nodal points of polygonal planes. In order to display the polygonal planes between the nodal points on a screen, the space coordinates for the nodal points are then converted from a 3-dimensional coordinate system, for example through central projection, to a 2-dimensional screen coordinate system.
Such an image processing method is known from ERNST, JACKEL, RUSSELER, WITTIG: "Hardware Supported Bump Mapping: A Step towards Higher Quality Real-time Rendering," 10.sup.th Eurographics Workshop on Graphics Hardware, Maastricht, Netherlands, 1995, 63-70. With this method, the brightness and color perception of the individual polygonal planes located between the nodal points of the grid model are calculated separately for each polygonal plane, by taking into consideration the angle of incidence of the light and the viewing direction of the viewer corresponding to a local illumination model. This method can take into account diffuse reflection and specular reflection at the polygonal plane.
When viewing an ideally reflecting surface, the viewer does not see the polygonal plane itself, but the environment around the object to be displayed, which is reflected in the polygonal plane. With the known image processing method, the intersecting point between a "visual ray," originating from the viewer and reflected at the polygonal plane, and a cubical enveloping surface that surrounds the spatial setting to be displayed is used to calculate the brightness and color perception developing as a result of the specular reflections at the polygonal plane. In this case, a brightness and color value is assigned to each element of the enveloping surface, so that the enveloping surface comprises an all-around picture of the environment from the perspective of the object to be displayed. In order to calculate the brightness and color perception of a polygonal plane of the grid model, it is only necessary to calculate the point of intersection for the "visual ray" reflected at the polygonal plane and the cubical enveloping surface, and to subsequently determine the brightness and color value corresponding with this point of intersection. The cubical enveloping surface in this case is reproduced with a storage matrix, which is addressed by the components of the "visual ray" present in vector form in order to determine the point of intersection of the "visual ray" and the enveloping surface. Each memory location of the storage matrix comprises the brightness and color value of a dihedral angle sector of the environment around the object to be displayed.
Thus, the determination of the brightness and color value occurring as a result of the specular reflection at the polygonal plane requires only several vector operations for calculating the point of intersection between "visual ray" and enveloping surface and a memory access to the storage matrix that reproduces the enveloping surface. The already known image processing method thus permits a relatively fast calculation of the image perception, which is important especially for a real-time rendering of movement displays.
The known image processing method has one disadvantage, however, in that only reflections of the "global" environment in the objects can be displayed, but not the reflections of interrelated objects among one another ("interreflections"). It is also not possible with the known image processing methods to display multiple reflections of the interrelated objects.